The present invention is directed to a method of stabilizing organic pigment particles, which had been previously surface modified, typically by exposure to plasma-activated process gases.
Due to the hydrophobic nature of organic pigment particles, it is difficult to disperse them in compositions, such as coating compositions or inks, such as ink jet inks. It has been known that pigment particle surfaces can be modified to increase their self-dispersibility in water or solvent borne compositions. One of the methods used for pigment surface modification is to add a surface modifier, either an ionic or non-ionic surfactant, such as an acid or glycol containing polymer, which permits the pigment to be fully dispersed in a composition. Another method used for pigment surface modification is to expose the pigment particles to ozone or plasma-activated process gases. One problem associated with plasma activated surface modification is that it results in creating highly exothermic sites on the surface of pigment particles that tend to rapidly react upon exposure to ambient air. As a result, it becomes unsafe to handle these highly exothermic surface modified pigment particles. Moreover, self-dispersibility of these highly exothermic pigments tends to suffer once the pigment has undergone the exothermic event.
The present invention solves the problem of unsafe, difficult to handle pigment particles that have been surface modified by exposure to ozone or the plasma activated gases.
The present invention is directed to a method of producing stabilized organic pigment particles, said method comprising:
surface modifying organic pigment particles;
contacting said surface modified particles with an aqueous vapor entrained in a carrier gas to produce said stabilized organic pigment particles.
The present invention is also directed to a device for producing stabilized organic pigment particles comprising:
a reactor,
means for introducing in said reactor aqueous vapor entrained in a carrier gas; and
an agitator assembly for deagglomerating said pigment particles placed in said reactor.